Fig. 3

QS signaling in Gram-negative bacteria and its role in biofilm formation. Autoinducer acylhomoserine lactones (AHLs) were commonly produced in Gram-negative bacteria communication and activated corresponding cytoplasmic receptors to modulate targeted genes expression. The canonical key regulators of QS system in Gram-negative bacteria is Luxl/luxR transcriptional factors, which could be activated by AHLs and therefore promoted target genes expression including virulence factors expression such as pyocyanin, lectin, elastase, proteases, toxin and so on. There are also other types of autoinducers (Pseudomonas quinolone signal (PQS), CAI-1, AI-2, etc.) and corresponding QS receptors (LasI/LasR, RhlI/RhlR, CqsS and LuxPQ, etc.) varied in different kinds of Gram-negative bacteria. The activated receptors by specific autoinducers finally promote genes expression such as adhesins and virulence factors, which are further involved in biofilm development